An ultrasonic sensor for a vehicle is normally arranged on a bumper or front grille, at which the likelihood of becoming wet is high and the vibration received is strong. Thus, in the prior art, a typical ultrasonic sensor uses a hydrophobic and flexible filler (silicon or the like) to fill the housing, which accommodates an electronic circuit substrate or the like. This ensures the required water resistance and vibration resistance (e.g., refer to patent literature 1).
However, the filling of a filler as in the prior art increases weight and cost. Additionally, due to the presence of the filler, the electronic circuit substrate has a tendency to become deformed. This may form cracks in portions soldered to the electronic components on the electronic circuit substrate. There is also a problem in that detection area property of the sensor may differ before and after the filling of the filler. Factors that deform the electronic circuit include, for example, external load resulting from the thermal expansion and contraction of the filler. An example of a differed detection area property would be a narrowed detection area. Moreover, much time is required to dry the filler. From such viewpoints, many improvements may be made.